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Thu, 02 Oct 2025 23:30:12 -0700 (PDT) X-Google-Smtp-Source: AGHT+IELR1JYmclf4EKUfrFyht98SyMCf4qSX9xmzaypmk8A7lQqrolOq939RWKtbUXsUaroq0t3UA== X-Received: by 2002:a05:6000:40dc:b0:3ec:dd27:dfa3 with SMTP id ffacd0b85a97d-42566c5354dmr1300929f8f.25.1759473012477; Thu, 02 Oct 2025 23:30:12 -0700 (PDT) Received: from gmonaco-thinkpadt14gen3.rmtit.csb ([185.107.56.40]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4255d8a6b40sm6443426f8f.2.2025.10.02.23.30.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Oct 2025 23:30:12 -0700 (PDT) Message-ID: <3c55441187b869b5bb07b74ef88c10bfd51f9fb1.camel@redhat.com> Subject: Re: [PATCH] rv: Add signal reactor From: Gabriele Monaco To: Nam Cao Cc: Thomas =?ISO-8859-1?Q?Wei=DFschuh?= , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers Date: Fri, 03 Oct 2025 08:30:10 +0200 In-Reply-To: <87ikgxqrna.fsf@yellow.woof> References: <20250919-rv-reactor-signal-v1-1-fb0012034158@linutronix.de> <20250922162900.eNwI7CS0@linutronix.de> <6a5fde33-b3e3-44e2-8ea5-5f4cf350cf35@linutronix.de> <87ikgxqrna.fsf@yellow.woof> Autocrypt: addr=gmonaco@redhat.com; prefer-encrypt=mutual; keydata=mDMEZuK5YxYJKwYBBAHaRw8BAQdAmJ3dM9Sz6/Hodu33Qrf8QH2bNeNbOikqYtxWFLVm0 1a0JEdhYnJpZWxlIE1vbmFjbyA8Z21vbmFjb0BrZXJuZWwub3JnPoiZBBMWCgBBFiEEysoR+AuB3R Zwp6j270psSVh4TfIFAmjKX2MCGwMFCQWjmoAFCwkIBwICIgIGFQoJCAsCBBYCAwECHgcCF4AACgk Q70psSVh4TfIQuAD+JulczTN6l7oJjyroySU55Fbjdvo52xiYYlMjPG7dCTsBAMFI7dSL5zg98I+8 cXY1J7kyNsY6/dcipqBM4RMaxXsOtCRHYWJyaWVsZSBNb25hY28gPGdtb25hY29AcmVkaGF0LmNvb T6InAQTFgoARAIbAwUJBaOagAULCQgHAgIiAgYVCgkICwIEFgIDAQIeBwIXgBYhBMrKEfgLgd0WcK eo9u9KbElYeE3yBQJoymCyAhkBAAoJEO9KbElYeE3yjX4BAJ/ETNnlHn8OjZPT77xGmal9kbT1bC1 7DfrYVISWV2Y1AP9HdAMhWNAvtCtN2S1beYjNybuK6IzWYcFfeOV+OBWRDQ== Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-2.fc42) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 2025-10-02T14:56:23Z Nam Cao : > Thomas Wei=C3=9Fschuh writes: >> I am wondering if it would make sense to add a new tracepoint that >> fires in addition of the reactors. That would allow multiple >> simultaneous consumers and also bespoke handlers in userspace. > > We do have tracepoints for each monitor in: kernel/trace/rv/rv_trace.h > > And yeah, I think it is a nice idea for all the consumers to use these > tracepoints intead (that includes rtapp testing, and also the existing > reactors). It would simplify things, as the monitors do not have to > worry about the reactors, they only need to invoke tracepoints. > > But this also makes me think about the necessity of the existing > reactors. What do they offer that tracepoints do not? Myself I almost > never use the reactors, so I'm thinking about removing them. But maybe > @Gabriele has objections? Well, many use cases might be better off with tracepoints, but reactors do things tracepoints cannot really do. Printk is much faster (and perhaps more reliable) than the trace buffer for printing, panic can be used to gather a kernel dump. One may just attach to tracepoints via libtracefs/BPF and do most of the th= ings you'd want to do with a new reactor, but I see reactors much easier to use = from scripts, for instance. LTLs don't benefit as much as they don't print any additional information v= ia reactors, but DA/HA give hints on what's wrong. I wouldn't get rid of reactors until they become a huge maintenance burden,= but probably we could think about it twice before extending or making them more complex. For instance, what's the exact use case of the signal reactor? Isn't it sim= pler to do everything in BPF? Is the signal needed at all or something else (e.g= . perf) would do the job? Thoughts? Gabriele